Transition from elastic instability to drag reduction observed in two-dimensional turbulent flow*

To detect the flow regimes of Newtonian turbulence (NT), elasto inertial filament (EIF), elasto inertial turbulence (EIT) and maximum drag reduction (MDR) of polymer solution and their transition have been a hot topic in the last decade. We attempted to detect NT, EIF, EIT, and MDR by visualizing vortex shedding downstream of an array of cylinders that was inserted perpendicular to polymer-doped two-dimensional flow (2D). Polymers are stretched at the cylinders, and therefore, vortex shedding is affected as the consequent of viscoelasticity. The flow regimes are characterized based on Weissenberg (Wi) and Reynolds numbers (Re) with the relaxation time of the polymeric solution. The flow regimes are observed for different molecular weights of polymers in solution and are categorized as either vortex type 1, type 2 and type 3 on a Re-Wi map based on flow visualization using particle image velocimetry (PIV). In addition, turbulent statistics of these flow regimes are calculated to more fully quantify these flow regimes. We found that vortex types from 1 to 3 have a similarity to NT, EIF, EIT and MDR. In addition, characteristic turbulent energy transfer without an increase in turbulent energy production was found in the flow regimes of vortex types 2 and 3 of each polymer solution.